Extend ALTERTABLETO allow FOREIGNKEYSTO be added WITHOUT initial validation.
FK constraints that are marked NOT VALID may later be VALIDATED, which uses an
ShareUpdateExclusiveLock ONCONSTRAINTTABLEAND RowShareLock ON referenced
TABLE. Significantly reduces LOCK strength AND duration WHEN adding FKs.NEW state visible FROM psql.
Simon Riggs,WITH reviews FROM Marko Tiikkaja AND Robert Haas